The greenhouse effect is real. If there were no greenhouse gases in the atmosphere, earth would be a cold place. Compare Mars versus Venus – Mars has minimal greenhouse gas molecules in its’ atmosphere due to low atmospheric pressure, and is cold. By contrast, Venus has a lot of greenhouse gas molecules in its’ atmosphere, and is very hot. Temperature increases as greenhouse gas concentration increases. These are undisputed facts.
outgoing radiation = incoming radiation – changes in oceanic heat content
The image below from AER Research explains the radiative balance.
http://www.aer.com/scienceResearch/rc/rc.html
About 30% of the incoming shortwave radiation (SW) is reflected by clouds and from the earth’s surface. 20% is absorbed by clouds and re-emitted back into space as longwave (LW) radiation. The other 50% reaches the earth’s surface and warms us. All of that 50% eventually makes it back out into space as LW radiation, through intermediate processes of convection, conduction or radiation. As greenhouse gas concentration increases, the total number of collisions with GHG molecules increases. This makes it more difficult for LW radiation to escape. In order to maintain equilibrium, the temperature has to increase. Higher temperatures mean higher energies, which in turn increase the frequency of emission events. Thus the incoming/outgoing balance is maintained.
Click for larger image
http://www.aer.com/scienceResearch/rc/m-proj/lbl_clrt_mls.html
The important greenhouse gases are: H2O, CO2, O3, N2O, CO and CH4. The reason why the desert can get very cold at night is because of a lack of water vapor. The same is true for Antarctica. The extreme cold in Antarctica is due to high albedo and a lack of water vapor and clouds in the atmosphere, which results in almost all of the incoming radiation returning immediately to space.
An earth with no CO2 would be very cold. The first few tens of PPM produce a strong warming effect, and increases after that are incremental. It is widely agreed that a doubling of CO2 will increase atmospheric temperatures by about 1.2C, before feedbacks. So the debate is not about the greenhouse effect, it is about the feedbacks.
Suppose that the amount of reflected SW from clouds increases from 20% to 21%? That would cause a significant cooling effect. Thus the ability of GCM models to model future temperatures is largely dependent on the ability to model future clouds. Cloud modeling is acknowledged to be currently one of the weakest links in the GCMs. Given the sensitivity to clouds, it is perhaps surprising that some high profile climate scientists are willing to claim that 6C+ temperature rises are established science.
So the bottom line is that the greenhouse effect is real. Increasing CO2 will increase temperatures. If you want to make a knowledgeable argument, learn about the feedbacks. That is where the disagreement lies.
David Porter (09:58:46) :
Steven,
Would it be possible to give an explanation/interpretation to the spectral cooling rate graphic shown in your discussion above. Alternatively could you provide a reference to read. BTW the link to AER does not provide the info, as far as I can tell.
It’s the radiational cooling of the atmosphere by altitude and wavenumber (& hence species).
S A Clough & M J Iacono, J Geophysical Research, vol 100, pp16519, 1995.
Note it’s not ‘GHG absorption by altitude and wavenumber’.
“Isn’t the effect of co2 logarithmic?”
It is debatable as to whether the effect is exactly logarithmic, but it is close enough, at least for the present concentration levels. It is important to realize that the water greenhouse effect is also logarithmic (at least according to MODTRAN). This probably helps to explain my connundrum about why it’s not hotter in Atlanta than in Daggett during July–there is still a sufficient amount of water vapor in Daggett to cause most of the “greenhouse effect,” so that the extra water vapor in Atlanta doesn’t add that much. By the same token, any additional water vapor that results from a 1.2 C heating from 2 X CO2 (about 8%, by my calcs) cannot possibly cause a significant “positive water vapor feedback.”
“The coldest winter I ever spent was my summer in San Francisco”
Mark Twain”
Yes. Your hands don’t feel so warm when you ride your bicycle in the winter, right? This is because the water vapor makes your hands much colder in winter. This is due to the fact that it has a thermal capacity about 4 times that of the rest of the air. Same reason it makes your hands feel warmer when the air is warmer. I doubt that it has anything to do with “backradiation.”
Gerald,
Sorry I meant to say that fog blocks SW (not LW) which is the dominant factor during the day. LW blocking is more interesting at night.
Timo,
Thanks for the timely article!
David Porter,
Spectral cooling is a tricky concept, but basically correlates with IR absorption. A reasonable explanation here:
http://books.google.com/books?id=6xUpdPOPLckC&pg=PA409&lpg=PA409&dq=spectral+cooling+rate&source=bl&ots=NnNKiOSiRA&sig=Fny7_S8C9BIAXbp6iWbOtPFesfc&hl=en&ei=SN6mSbW4OoK2sQOizvngDw&sa=X&oi=book_result&resnum=9&ct=result#PPA409,M1
george h. (06:22:56) :
“My understanding of the skeptic argument regarding saturation is this: At current CO2 concentrations, all of the available IR in the relevant bands (2.7, 4.3 and 15 µm) is already captured. This is about 8% of the whole IR spectrum, which means that 92% of the IR passes right through without being absorbed by CO2. If the entire atmosphere were composed of nothing but CO2, it would still only be able to absorb 8% of the radiant heat. So if all of the available IR in that spectrum is being captured at current concentrations or lower, then adding more CO2 to the atmosphere won’t matter a bit.”
Perhaps you can enlighten us all as to “how” this is “fundamentally flawed”
Since we’re talking about the earth’s outgoing IR radiation only the 15µm band is relevant, this covers approximately 25% of the radiated spectrum (not 8%). The absorption spectrum isn’t saturated (only at the line centers) so an increase in [CO2] causes an ~logarithmic response in the lower troposphere. It also ignores the fact that IR emitted from clouds passes through a higher, thinner part of the atmosphere.
A new paper by Nir J. Shaviv entitled:
Using the oceans as a calorimeter to quantify the solar radiative forcing
Abstract:
Over the 11-year solar cycle, small changes in the total solar irradiance (TSI) give rise to small variations in the global energy budget. It was suggested, however, that different mechanisms could amplify solar activity variations to give large climatic effects, a possibility which is still a subject of debate. With this in mind, we use the oceans as a calorimeter to measure the radiative forcing variations associated with the solar cycle. This is achieved through the study of three independent records, the net heat flux into the oceans over 5 decades, the sea-level change rate based on tide gauge records over the 20th century, and the sea-surface temperature variations. Each of the records can be used to consistently derive the same oceanic heat flux. We find that the total radiative forcing associated with solar cycles variations is about 5 to 7 times larger than just those associated with the TSI variations, thus implying the necessary existence of an amplification mechanism, although without pointing to which one.
In:
Shaviv, N. J. (2008), Using the oceans as a calorimeter to quantify the solar radiative forcing, J. Geophys. Res., 113, A11101, doi:10.1029/2007JA012989.
Bye,
TMTisFree
If you want the full, and I mean FULL picture of the Climate Change science, check this compilation by Ken Gregory of Alberta… http://members.shaw.ca/sch25/FOS/Climate_Change_Science.html
It is very complete and full of details.
Simon Evans,
During the last ice age, Chicago was thousands of feet deep in ice. Summers then were undoubtedly more than 4C cooler than they are now.
DocWat: That’s a good layman’s description of what’s going on. The problem in calculation comes from not knowing the specifics well enough. Knowing the specifics is 99%, and making the calculations is 1%
Steve: R.W. Wood debunked the idea that a greenhouse works by trapping radiation 100 years ago. If his experiments were wrong, please explain where his mistake was.
If he’s right, then the various posters have it right when they say: 1. More solar energy hitting the earth (higher solar flux or proximity to the sun) makes the earth warmer (and vice versa), 2. The albedo or land, sea, & ice determine how much of that energy is “usable” to warm the earth, and 3. A “thicker” atmosphere means convection energy loss takes longer, allowing the temperature to be higher.
warm puddle says:
Gerlich and Tscheuschner are wrong. This paper debunks some of what they claimed: http://lanl.arxiv.org/abs/0802.4324
I’m a physicist and their claim that the atmospheric greenhouse effect violates the 2nd law of thermodynamics is easily shown to be wrong. What the 2nd law says is that the net flow of heat would have to be from the (warmer) earth to the (cooler) upper atmosphere. G&T seem to believe that the idea that the earth is warmer with an IR-absorbing atmosphere than in its absence then implies that the net heat flow is in the other direction. However, that is not the case. The net flow is still from the earth to the atmosphere. The warming occurs because the case one is comparing to is the case when there is no IR-absorbing atmosphere and hence NONE of the radiation that the earth emits is returned to it. Thus, the fact that the atmosphere returns any of the radiative energy emitted back to the earth, even if it returns only a fraction of what it receives from the earth, is enough to cause the temperature to be higher than it would be in the absence of an IR-absorbing atmosphere.
Or, as is succintly stated here http://www.ems.psu.edu/~fraser/Bad/BadGreenhouse.html , “The surface of the Earth is warmer than it would be in the absence of an atmosphere because it receives energy from two sources: the Sun and the atmosphere.”
Steve Goddard says:
Global mean means just that, GLOBAL MEAN. Some places cooled by more than 4C – 7C and some places cooled less. The polar regions cooled the most and the tropics the least. There was also presumably more cooling over continents than over the oceans. There also may have been some seasonal differences although I am less sure about that.
I tackled this general subject a while ago and it can be found here:
http://co2sceptics.com/news.php?id=1562
http://www.wilderness-survival.net/desert-2.php
I’ll add yet another conflicting explanation.
The IPCC cites Held & Soden 2000 to describe the mechanism as due to the pressure difference between the average altitude at which IR radiates into space, and the surface. When air is compressed it gets hotter, which means that as it moves vertically it changes temperature, leading to the adiabatic lapse rate. As air near the surface is warmed, convection speeds up until the lapse rate is restored. The effective temperature at which the Earth radiates, and hence the temperature of the ‘top’ of the atmosphere, is fixed by the temperature at which the heat out as calculated by the Stefan Boltzmann equation is equal to the total heat in. The greenhouse effect is the difference between this top-of-atmosphere radiative temperature that would apply without atmosphere, and the surface temperature, which is hotter because of the adiabatic lapse rate. The greenhouse effect is nothing to do with “trapping” IR, it’s physical mechanism is pressure.
And the enhanced greenhouse effect is because increasing CO2 means the average height of emission is raised, so you’ve got a bigger pressure difference.
If temperature increased with altitude, then more CO2 would result in cooling. This shows even clearer that it isn’t a “trapping” effect.
And Venus works the same way, except that with 90 times more atmosphere and high altitude clouds, the emitting layer is more like 50 km up instead of only 5 km up, and so the pressure-induced temperature difference is massive. (Because of its higher albedo, Venus actually absorbs less energy from the sun than Earth, despite being closer.)
Oh, and the tropical troposphere ‘hotspot’ is a result of the water vapour feedback mechanism predicted to treble global warming. It’s absence is a blow not to the validity of CO2 greenhouse physics, but to the postulated feedbacks.
I’d like to hope that might help, but I’m afraid it will only add to the confusion.
coaldust says:
While I tend to agree that you are probably right, your argument is not airtight, as Hansen has pointed out. Firstly, the sun has gradually brightened over time. Secondly, Hansen argues that some negative feedbacks that operate at geologic timescales (mainly involving the GHGs themselves, I believe) could be inoperable here due to the very fast pace with which we are increasing the GHGs.
So, to summarize, the general scientific view has been that a true runaway cannot occur on earth at the moment…I.e., that the positive feedbacks are sufficient to magnify the effects of the GHGs but not enough to lead to an instability that would lead to a runaway effect. However, Hansen claims otherwise at least if we really go to town in burning all available fossil fuels…And, while I remain skeptical of his claim, I don’t think one can immediately dismiss it out-of-hand.
You can’t model a system with this many variables.
This is a moot debate!
Cap and Trade will be implemented.
Energy prices will go up.
“Smart” meters will be installed.
And while you back and forth on this,
…………you know what….forget it!
tmtisfree (09:44:54) :
The surface thus heats up and warms the air by conduction and convection.Second law of thermodynamic prevents that the cooler atmosphere could warm the warmer surface without work. It is just not possible that surface is additionally warmed by this re-radiation.
It is not the cooler air that warms the surface, but radiation that goes through the transparent air to reach the surface and be absorbed by the opaque ground.
Mark N (23:15:03) :
Unfortunately there is no simple explanation. We are dealing with atomic science and the way molecules of gas react when energised. H2O has a higher expansion ratio than CO2 when given the equivalent energy input per volume.
It follows that H2O has an exhilarated contraction when energy is lost or diluted.
At reasonably high temperatures compared with CO2 water molecules form bonds with other H2O molecules and become liquid.
CO2 doesn’t form these bonds until the energy level has fallen a long way below that of H2O.
On top of that pressure plays a part in deciding at what point both molecules start to bond.
If I’m wrong then I hope someone with someone will give a better explanation of why H2O is both a positive and negative feedback in our climate and CO2 is more or less benign.
The off shot is that H2O conserves energy in the lower troposphere but leaks huge amounts of energy in the upper troposphere.
I cringe everytime I hear ‘CO2 is a greenhouse gas and must be causing warming.’
Our climate system is much more complex than that, yet the entire AGW argument seems to boil down to that statement.
It is widely agreed that a doubling of CO2 will increase atmospheric temperatures by about 1.2C, before feedbacks.
Is there a citation for this based on strong science, or is it just one of those givens everyone agrees with but no one can precisely say why?
Steve McIntyre has been asking for such a citation for quite awhile now and has apparently given up on ever having one provided.
Is this explanation of the greenhouse effect based on the hypothesis developed by Arrhenius that was never validated (Arrhenius, 1896). I know of no successful attempts to test this hypothesis practically or theoretically, yet is seems to be wholly accepted as fact. Are there any modern works that prove a greenhouse effect as you explained exists?
The concept that extra co2 would enable more re-radiated energy to be directed back down to the earths surface has always troubled me, yes energy would be directed back on collision, but the net energy flow (warm to cold) would prevent it from going all the way back to the earths surface by collision. The re-emission argument fails when there is a net flow of energy in one direction. It is in breach of the 2nd law of thermodynamics and is essentially a perpetuem mobile of the 2nd kind. Surely radiative forcing forms only part of the GE, with atmospheric mass, stored energy and convection also being key factors.
Suggesting infrared energy that only penetrates the seas surface by 1mm can actually warm the sea is odd, especially when evaporation is considered. Leave a large glass container of water in the shade and one in the sun and see which one warms the most.
tmtisfree
Second law of thermodynamic does not prevent a body to be heated by radiation.
Radiation is not heat, it has no temperature.
jae (10:18:07)
What’s missing in the dry desert situation is that central pink column labeled: “sensible and latent heat” on “The annual mean global energy balance for the earth-atmosphere system” diagram. This is the energy necessary to change liquid water into gas (water vapor). This evaporative coooling has a significant effect on the ground temperature and may add to the cloud albedo as well. The lack of liquid water in the desert means that this cooling effect would be minimal.
None of this has much to do with the greenhouse effect though.
Steven Goddard (10:42:24) :
Simon Evans,
During the last ice age, Chicago was thousands of feet deep in ice. Summers then were undoubtedly more than 4C cooler than they are now.
Local variation being much greater than the global mean, most obviously in the case of northern hemisphere glaciation. For the LGM Stenni et al. 2001 found about 9°C in Antarctica, Dahl-Jensen et al. 1998 found about 21°C in Greenland, whilst Sarnthein et al. 2003 and Kucera et al. 2005 confirm
moderate cooling of tropical SST, generally 0°C to 3.5°C, and so on. There are plenty of other studies, of course, but I suggest my 4C to 7C change in the global mean is a fair summary.
Barry
If you google James Lovelock the second thing you’ll find is his website.
Here it is if you want to send him a letter.
http://www.jameslovelock.org/
thanks
Edward